Zhoushan multi-terminals voltage source converter based high voltage direct current （VSC-HVDC） project, with the most terminal number and the largest converter capacity in the world, will construct 5 ±200 kV converter stations with the total capacity of 1 000 MW, which are interlinked by cables. The complete design and key equipment of Zhoushan multi-terminals VSC-HVDC project were provided by China domestic company. The grid structure of Zhoushan will be enhanced and the reliability of power supply can be increased after the project being put into operation. This paper introduced the system scheme of Zhoushan VSC-HVDC project, including main connection of convertor station, operation modes, main circuit parameters, active and reactive power diagram, control and protection strategy, etc. The result has important reference value to the follow-up construction of high-capacity VSC-HVDC project in China.
Study on overvoltage and insulation coordination can provide basic technical support for the implementation of Zhoushan multi-terminals VSC-HVDC （voltage sourced converters based high voltage direct current） project. In order to determine the protection configuration of arrester scheme and the insulation level of equipment, integrated design was carried out and the main circuit parameters of the project were proposed, as well as the main wiring. According to the control strategy of Zhoushan multi-terminals VSC-HVDC project, the electromagnetic transient simulation model was established. The capacitance of sub-module in converters, the type of transformer, the inductance of arm reactors and DC reactors, the grounding modes and the selection of cable parameters all influenced simulation results significantly in the model. Based on the detailed research, the equipments’ parameters were selected and used for the overvoltage simulation, the insulation levels of main equipments were determined as well. As the key equipment in this project, the DC cable’s insulation margin was suggested to be 30% in order to ensure the safe operation, and its insulation level was finally determined to be 510 kV. The research results have been applied in Zhoushan multi-terminals VSC-HVDC project, which can provide references for other similar projects.
The overvoltage of lightning intruding wave is the important basis for determining equipment insulation level in DC transmission system converter station. This paper built the simulation calculation model of lightning intruding wave for ±160 kV Nan’ao three-terminal flexible DC transmission system at DC side, with using PSCAD/EMTDC software. Then, the maximum shielding failure current of DC transmission line was calculated by electrical geometry model （EGM） and the intersection method was used as the criterion for air gap flashover. Finally, the voltage stresses of pole bus equipment and connection cable were calculated for the convertor station after DC transmission line suffering from the lightning shielding failure and counterattack, and the equipment’s insulation level for lightning impulse was checked. The results show that the insulation margin of the equipment meets the requirements.
In order to quickly and efficiently calculated the maximum overvoltage of DC transmission line in MMC-HVDC （modular multi-level converter-high voltage direct current） transmission system under DC-side single-pole grounding fault, this paper detailed analyzed several corresponding equivalent calculation models. Firstly, the equivalent model I of MMC was built based on the law of conservation of energy, in which the MMC was split into AC-side equivalent circuit and DC-side equivalent circuit, and the former was composed of 2 controlled current sources and an ideal capacitor. Secondly, the equivalent model II of MMC was built with the consideration that the capacitor voltage of sub-module in MMC was almost unchanged under single-pole grounding fault and the DC transmission lines could be replaced by equivalent circuit model. Finally, a 400 MW/±200 kV digital simulation model was built based on the time-domain simulation software PSCAD/EMTDC, and verified the effectiveness of the 2 kinds of equivalent models.
The grounding methods for multi-terminal voltage source converter based high voltage direct current （VSC-HVDC） transmission system in Zhoushan were researched, and the grounding method for each converter station was determined, in which star ground reactance with neutral grounding resistor were recommended for Dinghai and Daishan converter station, while Y/Y converter transformer with neutral grounding resistor were recommended for Qushan, Yangshan and Sijiao converter station. On this basis, the overvoltage and insulation levels of converter station equipments were calculated. For Dinghai and Daishan converter station, the rated voltage of equipment at the ac side of the converter transformer is 220 kV, the lightning impulse insulation level for equipments at this zone are 950 kV. For the other three stations, the rated voltage is 110 kV, the lightning impulse insulation level is 450 kV; the insulation level of lightning impulse and that of switching impulse for AC equipment at the valve side of the transformer are 650 kV （or 750 kV） and 550 kV; insulations for 200 kV DC polar line are suggested to 650 kV （or 750 kV） and 550 kV respectively.
Both solid and air insulation structure are used in the modular multi-level converter （MMC） for flexible DC transmission, but air insulation structure is a relatively weak link, in which fault often occurs during actual operation or test, such as partial discharge, etc. With using 3-Dimensional finite element calculation method for electric field, the air insulation structure of MMC was analyzed based on the electric field distribution, in which the electric fields in the air gap between layers of converter, the air medium outside of converter and the air gap between the in commutation hall were calculated respectively. Based on the intensity and distribution of electric field in the air gap, the insulation strength of air insulating medium was analyzed, and the design of insulation structure was proposed for the converter.
This paper introduced the topological structure and working principle of modular multi-level converter （MMC）, and presented a new control method for MMC-HVDC （modular multi-level converter based high voltage direct current） based on voltage vector composition. The switching frequency of sub-module was high in the traditional control method for MMC, so the switching loss was also high. In the proposed control method, the switching frequency of sub-module could be reduced to power frequency, so the module switching loss was greatly reduced. Meanwhile, the voltage balance control strategy of module and the closed-loop control system of converter were designed for the control method, in which the module voltage could obtain good control along with power frequency switching. Simulation results show that, the switching frequency of module is lower, and the voltage fluctuation range is small, in the proposed control system, which can realize the closed-loop control of power, as well as has great value in theoretical research and engineering application.
In order to build power systems with strong disaster resistant ability, a risk assessment method was proposed for the power systems with various topological characteristics under ice storm. Mesh coefficients and cycle-length distribution were employed to describe the topological characteristics of power system, in order to analyze the influence of topological characteristics on power system risk and provide guidance for the topology planning of power system. The ice storm risk indices based on the minimum lost-load value and the global topological characteristics indices were presented. Finally the topological characteristics with disaster-resistant topology were proposed. Taking IEEE 30 Node network and improved network as examples, the testing results have shown that the power systems with higher mesh coefficients and higher proportion of short-length cycles will have smaller ice disaster risk.
Facing the development bottleneck of the traditional AC power distribution network, the researchers pay more and more attention to the DC power distribution for its advantages. The domestic researches focus on the steady-state analysis, failure analysis and protection, stable operation and power quality control, etc. The establishment of DC power distribution experimental system can provide simulated and experimental research for DC power distribution, which can promote the development of DC distribution technology. The structure and function of the DC power distribution experimental system are described at first. And then the detail description of simulation and dynamic platform were presented, as well as the preliminary design scheme for the DC power distribution experimental system.
Aimed at the problem of low accuracy of traditional method for power system short-term load forecast, this paper presents a method for short-term load forecasting based on BP-ANN（back-propagation artificial neural network）. The multiscale entropy method was used to analyze the short-term load data, whose results showed that the forecast points were related to both the prophase adjacent data and the periodical long-term historical load data. Meanwhile, with using autocorrelation analysis method, the suitable method for short-term load forecasting of Shaanxi power grid was presented based on BP-ANN, and applied in practical power system load. The results have shown that this method is simple, feasible, more practical, and with high precision.
The description and disposition of uncertain information in the substation locating and sizing of distribution network have always been highlighted difficulties during planning. For further research on this issue, the uncertainty of load, the uncertainty of substation and line investment, as well as the uncertainty of electrovalence was considered. According to the fuzziness and randomness of uncertain factors, the technology of random fuzzy simulation was adopted to weight their influences in the model, which also considered geographic information factors, transformer loss and interruption cost. A multi-population differential cultural algorithm based on chaotic knowledge migration was presented, which designed four kinds of spatial knowledge guide evolution. And knowledge migration interval was dynamically adjusted according to evolution time. Then chaos sequence was used to deeply explore migrated units for the improvement of the validity of migrated knowledge. Finally the location case proves that the proposed model and method are correct and effective, and boast certain practical value.
Based on the precision and strength requirements, mechanical sensor was designed for icing online monitoring. The strain and stress of mechanical sensor were analyzed through the finite elements in order to optimize its structure and improve its anti-bending strength. Then, with the signal processing, the physical signal of sensor was transformed into the electric signal of data acquisition and control process, so as to complete the detection of icing conductor gravity. This mechanical sensor has been installed and has operated on Zila DC 400 kV transmission lines.
There are much higher technical requirements on composite insulators used in Qinghai-Tibet project, which is located in the plateau area with high altitude and strong UV radiation. According to the characteristics of high UV radiation in the region, the formulation optimization of silicone rubber for composite insulator was performed; furthermore, a 2 000 h UV aging test was carried out on silicone rubber before and after the improvement. The results show that the mechanical and electrical performance of silicone rubber, such as tensile strength, elongation ratio, volume resistivity and hydrophobicity, have been improved significantly after the formulation optimization, which can satisfy the use requirement of Qinghai-Tibet project. Then, this paper analyzed the UV aging mechanism and aging time trend of silicone rubber, whose results showed that the side chains of silicone rubber were cut by UV radiation and the crosslinking reaction happened to accelerate the aging process; however, UV radiation almost had no influence on the main chain of silicone rubber. Furthermore, there was a rapid decrease in the performance of silicone rubber during the initial aging period and the change tended to be stable after some time.
Though the rotary clamp conductor spacer-dampers have been widely used in extra high voltage （EHV） and ultra high voltage （UHV） transmission lines, the anti-galloping effect of this kind of spacer still needs to be studied. According to the design and parameters of spacer-damper, the anti-galloping mechanism of the spacer had been researched and verified. Since part of the rotary clamp conductor spacer-damper can rotate, so that the sub-conductor can rotate around its own axis, therefore the cross-section of iced conductor becomes uniform, which plays a role of galloping inhibition. Moreover, a three-dimensional finite element model of the conductor spacer system was established by means of ANSYS software. Based on the modal analysis of the conductor spacer-damper system, the natural frequencies and their vibration mode graph of the first 6 modes of this conductor spacer-damper system were obtained. According to the analysis of the natural frequencies and vibration types, it shows that the rotary clamp space-damper has a better effect on anti-galloping. On this basis, a suggestion for engineering application of this rotary clamp conductor spacer-damper was proposed.
In order to reduce the construction investment of large scale hydropower station, taking Gezhouba Dajiang hydropower station and Xiluodu Left Bank project as examples, this paper simulated and calculated the lightning invasion waves with using EMTP program. The calculation results show that the hydropower station which the connection between main transform and switch station uses overhead line can cancel the installation of arresters at busbar, but arresters should be installed at main transform; the hydropower station which the connection between main transform and switch station uses gas insulation line （GIL） can make busbar and main transform share a set of arresters. The large scale hydropower station always has lot of main transformers, and the arrester price of the gas insulated switchgear （GIS） in main transformer is expensive. So the optimization of GIS arrester in main transformer can bring great economic benefits. With the use of the optimized arrester arrangement scheme, the lightning protection reliability of 500 kV large scale hydropower station can be high enough.
Taking the coordination control logic in Baicheng power plant of china power investment corporation （CPI） as an example, this paper introduced the coordinated control system of large-scale supercritical thermal power unit, focused on the application of main steam pressure deviation tolerance method in the turbine control system, and analyzed the working process of this method in load rising stage as well as in load decreasing stage. The practical application proved that the pressure deviation tolerance method can quickly respond the load change, maximize the ability of turbine main control system in the process of power regulating. And it provides a final limit to the pressure deviation and make sure the serious pressure control will not happen, which has good control effect.
This paper described the principle of generator stator ground protection based on third harmonic, and pointed out that the protection parameters were affected greatly by the primary system parameters, especially the capacitor of GCB. Then the problems of generator stator ground protection based on third harmonic in projects were described and the impact of GCB capacitor on the stator ground protection was analyzed. The results show that the capacitor of GCB will educe the setting values of third harmonic. Finally, this paper presented the matters that should be paid attention during the field measurement and parameter setting of project protection.
The boiler combustion system in coal-fired power plant is a so complicated and important system that it is difficult to build a precise and adaptable model for it. First, the input and output data of combustion system collected from the scene was processed and selected for the combustion system modeling. Second, the Echo State Network （ESN）, which was a new type of Recurrent Neural Network, was improved and its precision and adaptability were increased. Then, the improved ESN was applied to building static model of combustion system, which had best adaptability compared with models founded with other four Neural Networks. Last, the improved ESN was applied to building dynamic model of combustion system, which had better adaptability and was more suitable for long-time prediction compared with static model.
Along with the diversification of project construction technology, the conventional evaluation model of power transmission project cost based on unit cost cannot meet the requirements of accuracy, comparability and so on, and it is lacking of instructive and practical operation ability in actual engineering cost management. In order to further improve the breadth and accuracy of the project cost index system, in consideration of the project’s characteristic factors, this paper established a three-level evaluation index system for power transmission project with using principal component analysis （PSA） and support vector machine （SVM） method, based on collecting & processing the sample data of power transmission project, and digging the key influencing factors of project cost. Then, the index evaluation model that could reflect the general rules of power transmission project cost was established, and the safety zone of each indicator was calculated. The sample test results show that the index evaluation system can control the evaluation error within 10%, which can provide more reliable reference information for project cost management.
In order to achieve the comprehensive schedule risk management of grid project, based on enterprise risk management （ERM） framework, a comprehensive schedule risk management system was formed, which concluded five subsystems: target system, environment system, organization system, process system and method system. Meanwhile, it presented the risk research method with circular transmission. Further, based on the research framework, it explored the risk link relations on the base of a new concept of “risk map” and built a risk evaluation model, then quantified the impact of each risk value via fuzzy evaluation. Finally, key risk with higher degree of influence was obtained, which could provide a reference for risk prevention and control.
